Process of treating gas



Jan. 25, 1955 w QDELL 2,700,600

PROCESS OF TREATING GAS Original Filed May 17, 1946 United States PatentO PROCESS OF TREATING GAS William W. Odell, Amherst, Va.

Continuation of application Serial .No. 670,409, May 17, 1946. Thisapplication January 16, 1952, Serial No. 266,614

16 Claims. (Cl. 48-197.)

This invention relates to a substantially continuous process of treatinggases and removing gum-forming hydrocarbons, nitrogen oxides,hydrocyanic acid and other impurities from gases containing saidimpurities. It particularly relates to the treatment of gases at highertemperatures than commonly used in purifying city gas for such useswhere a high degree of purity is required, which gases usually containhydrogen and frequently contain a hydrocarbon as an undesired component.

This application is .a continuation of my application Serial No.670,409, filed May 17, 1946, now abandoned.

It is understood that applicant does not desireto limit this inventionto the treatment of gases containing very small amounts of impuritiesand hydrocarbons; it can be used successfully with gases containing verylarge amounts of such materials or containing substantially largeamounts of vapor phase hydrocarbon.

One of the objects ofthisinvention is .the production Of a gas of high.degree of purity from water gas, reformed gases made by reactinghydrocarbons contained in the gas with both steam .and oxygen, and othergases which initially contain an appreciable percentage of hydrogen.Other objects will become apparent from the :dis closures made herein.

In the manufacture of ordinary water gas, forexample,

the major components are hydrogen and carbon monoxide n the espectiveamounts of about fifty and forty percent. However, besides thesecomponents there are present, usually, small amounts of impurities suchas H28, CS2, thiophene', mercaptans, organic sulphides, hydrogencyanide, olefins, diolefins, methane and other undesired materials. Inpresent practice the H28 is largely removed by absorption in water, analkaline solution, or by reaction with iron oxide. Organic sulphur islargely removed in common practice by absorption in active .carbon oroil washing. One known procedure for removing organic sulphur is bycontacting the gas with a catalyst comprising thirty percent sodiumcarbonate and approximately seventy percent iron oxide; the reactionbeing conducted at about 180 to 200 C, In the latter operation thesodium carbonate is converted to sulphate and then new catalyst isrequired, ,So .far as the inventor is aware a truly satisfactoryprocedure for removing the gum-forming components has not heretoforebeen provided. In the practice of this invention an eeomonical procedureis provided in which catalyst need not be thus consumed and one whichdoes not require-separate heat exchangers to economize the sensible heatof the gas. For highest degree of purification and conversion it isusually preferable in the practice of this invention that the gastreated be first subjected to a rough cation for the removal of themajor portion of the H28, particularly if the gas to be treatedinitially. contains large amounts of it.

This invention is particularly applicable to the treatment of gases athigh temperatures preferably in the presence of steam or otherendothermic oxidant such as CO2 and a relatively small amount of anexothermic oxidant such as oxygen or air, whereby the desired conversionor decomposition of impurities is accomplished.

One'form of apparatus in which this invention may be practiced is showndiagrammatically, in elevation in the figure which in essence is a flowdiagram.

In the figure the reaction chamber 1 with grate 12 is filled with sizedsurface contact solids 2, which may be spherical or otherwise shaped, orbroken solids of subor so-called coarse purifistantially uniform size,forming a deep bed. The gas to be treated is supplied through conduit 3and three-way valve 8 which so controls the directionof gas flow to andthrough chamber 1. Thus gas from 8 may flow upwardly through conduit 9,down through the bed of solids in chamber 1, out at the bottom of 1,through valve 15 and conduit 16 and out to a cooling system through 17and valve 30, or it may pass from 8 downwardly through conduit 10, upthrough the bed of solids in chamber 1 and out at the top of 1, throughtake 17 and valve 30. The direct-ionof flow is controlled by operatingvalves 8, 13 and 15. Oxygen or air, as the case requires, is admittedthrough conduit 4 and valve 5, whereas steam is introduced throughconduit 6 and valve 7. Thermocouples, suitably connected to indicatetemperatures, are shown at 19, '20, 21 and 22. Means for supplying .airfor starting operations comprise conduit '24, valve 25 and ignition door27. Valve 28 controls the :fiow of gas to stack 29 and valve 30 controls'the how of gas toa suitable holder or-gas system.

Operations according to this invention are shown by examples as follows:

EXAMPLE 1 Removal of gum-forming hydrocarbons and CH4 from water gasmade from coal, incompletely carbonized coal .and the like, composedchiefly of H2 and CO but containing approximately 1.8 percent of CH4 and0.2 percent of 'illuminants which latter includes the gum-formingconstituents, and '8 grains per cubic feet of organic sulphur compounds.Chamber 1 is filled with care fully selected sol-ids, preferably about 1inch mean diameter in large reaction chambers and preferably spheri-.cal, which may the chiefly SiOz, A1203, CrzOs or other highlyrefractory material. The size of the solids should preferably'beappreciably smaller than 1 inch mean diameter in small size reactors.Combustible fuel gas (the water gas to be treated is satisfactory) iscaused to How through 3 by opening valve 11 and an excess of air for itscombustion is admitted by opening valve 25. Valve 8 is so opened thatthe gas flows through '8 and 10 to the bottom of 1 where it mixes withair; the mixture being burned in 1 after it is ignited through ignitionport 27. Combustion is continued and the air and gas ratios Varied sothat an appreciable thickness of bed 2 is heated to 1800 to 2300" F.meanwhile removing the products of combustion through 13, 14, 17, 28 and29, valve 30 being closed. The gas valves 11 and 8 are now closed and astraight air blast is made removing the air similarly through 13, 14,17, '28 and 29. The solids in the lowest at about atmospherictemperature; a higher zone is now t e hot zone in which the solids areheated to l800 to about 2300 F. and the top-zone solids are atsubstantially less than 300 to 400 F. The apparatus of the figure is nowready for regular opera tion. Valve 30 is now opened and valves 28 and25 are closed, water gas is admitted by opening valve 11, steam 18introduced by opening valve 7 and a very small amount of oxygen or airis admitted by opening valve 5. The sethrough 9, 1, 15, 16, 17 and valve30.

perature of the outlet gas from 1 reaches 400 F. another reversal offlow through reaction chamber 1 is initiated. The process is continuousand the temperature is self-sustaining and the heat wave or hot zonetravels alternately upwardly and downwardly through the bed of solid 2.It may be desirable at infrequent time intervals (periodically) to makea prolonged air blast to about 300 to valve 13, conduit 14 and otfthestack by opening valve 25 allowing the outlet blast gas temperature torise above 300 F. and admitting a small amount of gas through 11, 8, andto 1, during a late stage of the air blast period. The gas-air mixtureat this stage may be 1 volume of gas and to volumes of an.

During the regular gas-treating operation the proportions of 02, gas andsteam used in this example are:

Cubic feet Water gas 1000 Steam 100 Oxygen 12 The pressure in thereaction chamber and system may be substantially atmospheric pressure or10 to 20 atmospheres or more may prevail. One of the advantages of theuse of superatmospheric pressure is that smaller equipment and lowerlinear velocities through the contact solids may be employed. Somewhatmore steam is de sired when operating under superatmospheric pressurethan at atmospheric pressure to prevent carbon formation, although 200cubic feet of steam per 1000 cubic feet of water gas is usually ampleeven at 20 atmospheres pressure. There is no apparent advantage inappreciably preheating the gas or oxygen but the steam used should be atsuch a temperature relative to the oxygen and water gas thatcondensation of water vapor does not occur in the inlet conduits to thereaction chamber; the steam-gas mixture may enter the reaction chamberbelow 200 F. The linear velocity of the fluid stream into the bed ofsolids in the reaction chamber, calculated as at 60 F., may be of theorder of 110 cubic feet per minute per square foot of equivalent gratearea, namely per square ioot of internal horizontal sectional area ofsaid chamer.

The size of the solids used should be proportioned to the diameter ofthe reaction chamber; a size of about 0.75 to 1.5 inches mean diameteris satisfactory for large chambers having an internal diameter of 8 to10 feet, whereas with chambers 4 to 5 feet internal diameter the sizesolids preferred is 0.3 to 0.8 inch. Although the solids should be asuniform in size as possible in order to minimize the wall effect" and tominimize the necessity of periodically driving the heat to substantiallyone end of the reaction chamber, it is decidedly advantageous to employmetal spheres or the like at the top and bottom layers and these can besmaller than the other solids. The metal being a better conductor ofheat than the ordinary refractory solids is perhaps an explanation ofthe leveling out effect of the metal solids on the T zones. Thetemperature zones should be horizontal layers; the use of metal in thetop and bottom layers is helpful in maintaining this condition.

The results obtained in this Example 1 are indicated by gas analyses asfollows:

Composition of the moisture free gases Inlet Outlet Water Treated GasGas Organic sulphur-Grains per 100 cubic feet 8 Trace The gum forminghydrocarbons which were present in the raw water gas were entirelyeliminated and the volume of combustible gas was increased 4 percent.Apparently oxidation, and re-forming reactions occur in the reactionchamber in a very efiicient manner. Some of these reactions which canoccur are:

Diolefins polymerize, split, oxidize and also react with hydrogen toform saturated hydrocarbons which in turn are re-formed by reaction withsteam to form CO and H2 or with O2 to form CO and H2. Likewise Reaction6 proceeds at quite low temperatures. Thus small amounts of hydrocarbonsmay be eliminated and the total volume of CO+H2 increased simultaneouslywith the elimmation of nitrogen oxides and gum-forming substances.

The invention is not limited as to the velocity of flow of fluidsthrough the bed of solids. However, the time of contact of the fluidswith the hot solids will vary according to the temperature of the solidsand the nature of the gas being treated; experiments with a given gas ata chosen temperature will establish a possible limit.

The temperatures given in the example are those found to be satisfactorywithout the use of catalyst solids. OX1- dation catalyst can be used atlower temperatures, particularly with some gases. Thiophene and some gumformers are best destroyed by high temperature treatment as described.

Coal gas or mixtures of water gas and coal gas may be similarly treatedand the methane and ethylene and traces of other hydrocarbons areconverted to hydrogen and oxide of carbon. As in Example 1 the use ofsteam preferably is in excess of the chemical requirements to satisfyreactions such as those indicated by Equations 3, 4, 6 and 13.

It will be noted that the stream initially containing the reactantfluid, in passing through the bed of prepared small size solids, as inreaction chamber 1 of the figure, first contacts relatively cool solidsand as its travel continues its temperature is raised, layer by layer,to the maximum temperature in the hot zone of said bed and is thensimilarly cooled to a similar lower temperature. As the streamtemperature rises in its travel through the bed it reaches a temperaturewhere reactions such as shown in Equations 1, 2, 11 and 12 occur at amuch faster rate than the steam hydrocarbon reactions and this is a verydesirable condition; the endothermic reactions proceed rapidly only athigher temperatures, above about 1650 F. without a catalyst. Therefore,in promoting chemical reactions in a gas stream by this invention theoxidation of the hydrocarbons by oxygen is initiated before theoxidation of hydrocarbons by C02 or steam.

in most processes, so far as I am aware, the substitution of CO2 forsteam as a reactant for hydrocarbon conversion is not particularlyadvantageous since the heat required is substantially the same in eachcase, i. e., Equations 3 and 5. However, in this invention, and in thepreparation of a synthesis gas for example, CO2 is usually washed out ofthe raw gas made and is discarded. Its use in this invention isindicated to the extent it is available and to the limit placed by anyparticular ratio of Hz to CO in the synthesis gas. Lower inlet andoutlet temperatures can be used in this invention when C02 18 employedreplacing an equivalent of steam.

A catalyst may be used in any portion of the bed or the bed may becomprised substantially entirely of catalyst material. It should beselected in accordance with the sulphur content and other properties ofthe gas to be treated.

Although any operable temperature above about 1650 F. to 1850 may beemployed a range found to be satisfactory and preferred is above about1800 F. and not appreciably above 2300 F. A catalyst is not required atthe latter temperatures.

Referring to the figure chamber 1 may be so designed that the bed ofsolid confined therein tapers downwardly 1n the lower portion thereof asmentioned in my Patent No. 2,494,576, dated January 17, 1950, relatingto a process and apparatus for making combustible gas, and tapersupwardly in the upper portion thereof.

Having described my invention so that one skilled in the art canpractice it with variations to suit a particular gas to be treated or toproduce a particular finished beneficiated gas, I claim:

1. A process for treating a gas mixture containing a hydrocarbon toeffect conversion of said hydrocarbon, wh ch process comprisespreliminarily heating an interestates mediate maximum temperature hotzone of an uprightreaction chamber containing a continuous deep bed ofsmall size solids by passing a combustible gaseous mixture lengthwisethrough said bed of small size solids, burning said combustible gaseousmixture in passing through the bed and continuing the combustion untilan appreciable thickness of the bed is heated to a temperature of from1650 F. to 2300 F., meanwhile removing the. products of combustion fromthe reaction chamber, then discontinuing the combustion and passing acooling fluid lengthwise through the bed until the solids near the pointof introduction of the cooling blast-are at about the temperature of thecooling fluid, the temperature of the solids at the opposite end of thechamber is below about 300 to 400 F., and the temperature of the solidsat the intermediate hot zone of said bed is within the range of 1650 toabout 2300 F.; then subjecting the gas to be treated for conversion ofhydrocarbon to contact with the solids in said reaction chamber, bypassing the gas mixture initially containing the hydrocarbon inadmixture with free oxygen and a member of a group consisting of steamand CO2 lengthwise through the entire bed of solids in said reactionchamber from the end thereof having a temperature below about 300 to 400F. through the hot zone whereby conversion of the hydrocarbon iseffected, and withdrawing the resulting products from the opposite endof the reaction chamber from the point of entry, the amount of oxygen inthe gas mixture being just suflicient to maintain the temperature of1650 to 2300 F. in the hot zone, and the total amount of oxygen andsteam used being sutficient for the conversion of said hydrocarbonsubstantially without the production of carbon black.

2. A process for treating a gas mixture containing a hydrocarbon toeffect conversion of said hydrocarbon, which process comprisespreliminarily heating an intermediate maximum temperature hot zone of anupright reaction chamber containing a continuous deep bed of small sizesolids by passing a combustible gaseous mixture lengthwise through saidbed of small size solids, burning said combustible gaseous mixture inpassing through the bed and continuing the combustion until anappreciable thickness of the bed is heated to a temperature of from1650" F. to 2300 F., meanwhile removing the products of combustion fromthe reaction chamber, then discontinuing the combustion and passing acooling fluid lengthwise through the bed until the solids near the pointof introduction of the cooling blast are at about the initialtemperature of said cooling fluid, the temperature of the solids at theopposite end of the chamber is below about 300 to 400 F., and thetemperature of the solids at an intermediate hot zone is about 1650 toabout 2300 F.; then subjecting the gas mixture to be treated forconversion of hydrocarbon to contact with the solids in said reactionchamber, by passing a stream of the gas mixture initially containing thehydrocarbon in admixture with K free oxygen and a member of a groupconsisting of steam and CO2 lengthwise through the entire bed of solidsin said reaction chamber from the end thereof having a temperature belowabout 300 to- 400 F. through the hot zone whereby conversion of thehydrocarbon is effected, and withdrawing the resulting products from theopposite end of the reaction chamber from the point of entry, the amountof oxygen in the gas mixture being just suflicient to maintain thetemperature of 1650 to 2300 F. in the hot zone, and the total amount ofoxygen and steam used being suflicient for the conversion of saidhydrocarbon without the production of carbon black, and reversing thedirection of flow of the gas stream being treated when the temperatureof the outgoing gases reaches about 300 to 400 F.

3. A continuous process for treating a gas mixture containing ahydrocarbon to effect vapor phase conversion of said hydrocarbon, whichcomprises initially establishing in a confined deep upright continuousbed of small sized solids a hot intermediate maximum temperaturereaction zone having an elevated temperature substantially Within therange of 1650 to 2300 F. by burning combustible gases therein, andestablishing cool top and bottom end zones wherein the solids have atemperature substantially below 300 to 400 F. at the outer ends, thenpassing a gasiform fluid stream initially at a temperature substantiallybelow 300 to 400 F. and initially containing a hydrocarbon constituentin vapor phase together with an endothermic gaseous oxidant selectedfrom a group consisting of steam and C02 and a smaller quantity of an 6exothermic oxidant selected from a group consisting of oxygen and air,lengthwise completely through the bed of solids in one direction withoutaddition of other fluids to the bed of solids, whereby a portion of thehydrocarbon is convertedin said intermediate maximum temperature hotzone by reaction with said endothermic oxidizing gas and a part isexothermically oxidized to maintain the temperature of the intermediatereaction zone, removing the resulting fluid mixture from the bed at theend opposite 'the point of entry of the gasiform fluid stream at atemperature not exceeding 300 to 400 F., continuing the passage of thegasiform fluid stream to be treated in the same direction through thebed of solids until the temperature of the outgoing gases reaches about300 to 400 F., then reversing the direction of flow through the bed andrepeating the reversal whenever the temperature of the outgoing gasesreaches about 300 to 400 F., the quantity of the exothermic oxidant inthe gasiform fluid stream being just sufiicient to continuously maintainthe temperature in the hot reaction zone substantially within the rangeof 1650 to 2300 F. and the total quantity of gaseous oxidant beingsuflicient for conlgiersigm of the hydrocarbon without production ofcarbon 4. A process as set forth in claim 3 wherein substantiallyuniformly sized contact solids are employed in the intermediate hot zoneand metallic solids of smaller size than the solids at the intermediatezone are employed adjacent the ends of the upright bed.

5. A process as set forth in claim 3, wherein the quantity of theendothermic oxidant is about 10 to 20% by volume of the gas mixturecontaining the hydrocarbon.

6. A process as set forth in claim 3 wherein the quantity of theexothermic oxidant is about .2 to 5% by volume of the gas mixturecontaining the hydrocarbon.

7. A process as set forth in claim 3, wherein the gas mixture undergoingtreatment is water gas containing relatively small quantities ofilluminants and methane as impurities.

8. A process as set forth in claim 3, wherein the gas mixture undergoingtreatment contains a large quantity of vapor phase hydrocarbon.

9 A process as set forth in claim 8, wherein the endothermic oxidant issteam and is employed within the range of 10 to 20% by volume of the gasmixture undergoing treatment.

10. A process as set forth in claim 3, wherein substantially atmosphericpressure is maintained within the reaction chamber.

11. A process as set forth in claim 3, wherein superatmospheric pressureof approximately 10 to 20 atmospheres is maintained Within the reactionchamber, thereby permitting lower linear velocities of the gases throughthe contact solids.

12. A process as set forth in claim 3, wherein CO2 is included in theendothermic oxidant to permit the use of lower inlet and outlettemperatures.

13. A process as set forth in claim 3, wherein the bed of solids iscomprised of catalytic material.

14. A process as set forth in claim 3, wherein the temperature of thehot zone is within the range of 1800 F. to 2300 F. and the process iscarried out without the use of a catalyst.

15. A process as set forth in claim 3, in which the direction of flowthrough the bed of solids of the gasiform fluid stream undergoingtreatment is periodically reversed whereby the hot zone travelsalternately upwardly and downwardly through the bed of solids.

16. A continuous process of treating a gaseous mixture containing ahydrocarbon to effect vapor phase conversion of said hydrocarbon atelevated temperatures comprising first establishing a single deepcontinuous stationary bed of small contact solids in a reaction chamber,establishing a miximum temperature reaction hot zone having theapproximate range of l650 to 2300 F. intermediate the top and bottom ofsaid bed of solids, and establishing cool top and bottom zones whereinthe solids have a temperature substantially below 300 to 400 F. at theouter ends passing a gasiform fluid stream initially containing saidhydrocarbon reactant mixed with an endothermic gaseous oxidant selectedfrom a group consisting of CO2 and steam, and an exothermic gaseousoxidant selected from a group consisting of air and oxygen alternatelyentirely through the bed from one end to the other without addition offluid intermediate the ends of the bed,

in 8 the amount of endothermic oxidi in a Present be n SUbStfllfifl-HYless than the volume of the gas mixture e ng treate the amount ofexothermi oxidant initially pr sen in the gasitormflnidstream being.bstantially le s thanv tha oi-the endothermic gas but sutfiei n to mainain said high temperature in the high temperature zone only, and thetotal quantity of gaseous oxidant being just suflicient for 0 conversionof the hydrocarbon substantially without production of carbon black,making the alternations from Rejienenges Cited in the file of thispatent UNITED STATES PATENTS up runs to down runs periodically as thetemperature of 1,919,857 Pier et al July 25, 1933 the gas leaving thebed reaches a temperature approximat- 2,121,733 Cottrell June 21, 1 938ing 300 to 400 F., thereby promoting reaction of said 10 2,421,744Daniels June 10, 1947 reactant hydrocarbon in said stream within the hotzone FOREIGN PATENTS while maintaining the top and bottom Zones attcmperatures considerably below that of the intermediate hot zone,390,849 Great Britain Apr. 5, 1933

1. A PROCESS FOR TREATING A GAS MIXTURE CONTAINING A HYDROCARBON TOEFLECT CONVERSION OF SAID HYDROCARBON, WHICH PROCES COMPRISESPRELIMINARILY HEATING AN INTERMEDIATE MAXIMUM TEMPERATURE HOT ZONE OF ANUPRIGHT REACTION CHAMBER CONTAINING A CONTINUOUS DEEP BED OF SMALL SIZESOLIDS BY PASSING A COMBUSTIBLE GASEOUS MIXTURE LENGTHWISE THROUGH SAIDBED OF SMALL SIZE SOLIDS, BURNING SAID COMBUSTIBLE GASEOUS MIXTURE INPASSING THROUGH THE BED AND CONTINUING THE COMBUSTION UNTIL ANAPPRECIABLE THICKNESS OF THE BED IS HEATED TO A TEMPERATURE OF FROM1650* F. TO 2300* F., MEANWHILE REMOVING THE PRODUCTS OF COMBUSTION FROMTHE REACTION CHAMBER, THEN DISCONTINUING THE COMBUSTION AND PASSING ACOOLING FLUID LENGTHWISE THROUGH THE BED UNTIL THE SOLIDS NEAR THE POINTOF INTRODUCTION OF THE COOLING BLAST ARE AT ABOUT THE TEMPERA TURE OFTHE COOLING FLUID, THE TEMPERATURE OF THE SOLIDS AT THE OPPOSITE END OFTHE CHAMBER IS BELOW ABOUT 300* TO 400* F., AND THE TEMPERATURE OF THESOLIDS AT THE INTERMEDIATE HOT ZONE OF SAID BED IS WITHIN THE RANGE OF1650*